DONETSK, Ukraine — Ukraine’s new president-elect on Monday promised to negotiate an end to a pro-Russia insurgency in the east, saying he was willing to begin talks with Moscow, while the Kyiv government launched an airstrike on militants who occupied a major airport.

Russia quickly welcomed Petro Poroshenko’s offer for talks, raising hopes that his election will indeed ease the protracted crisis that has fueled tensions unseen since the end of the Cold War.

But Ukraine’s military launched airstrikes Monday against separatists who had taken over the airport in the eastern capital of Donetsk in what appeared to be the most visible operation of the Ukrainian troops since they started a crackdown on insurgents last month.

In Donetsk, a city of one million, sustained artillery and gunfire was heard from the airport. Fighter jets and military helicopters were seen flying overhead, and dense black smoke rose in the air.

An Associated Press journalist saw several vehicles full of dozens of heavily armed men arrive to the area adjacent to the airport. Half an hour later, several flatbed trucks full of reinforcements came in.

Vladislav Seleznyov, a spokesman for Kyiv’s anti-terrorist operation, wrote on his Facebook account that the military had given an ultimatum to the armed men who had occupied the airport to lay down their arms. He said the gunmen didn’t comply and the military launched an air strike.

Denis Pushilin, a leader of the separatists, said they had sent their men to the airport after some of their supporters were detained.

Many flights to or from Donetsk were delayed or cancelled on Monday. Access to the airport was blocked by police.

In Kyiv, international observers hailed Ukraine’s presidential vote as a “genuine election,” saying it was held freely and fairly.

Candy magnate Poroshenko, known for his pragmatism, supports building strong ties with Europe but also has stressed the importance of mending relations with Moscow. Upon claiming victory in Sunday’s vote, he said his first step as president would be to visit the Donbass eastern industrial region, where pro-Russia separatists have seized government buildings, declared independence and battled government troops in weeks of fighting.

“Peace in the country and peace in the east is my main priority,” Poroshenko said Monday, signalling that he would bring to an end the Ukrainian army’s much-criticized campaign to drive out the armed pro-Russia separatists.

The tycoon looked decidedly cool and composed Sunday night when the exit poll results were announced. On Monday, he got emotional when he was asked about the crisis in the east.

“The anti-terrorist operation cannot and should not last two or three months,” he said. “It should and will last hours.”

The military operation has caused civilian deaths and destroyed property — angering many eastern residents — while still failing to crush the rebellion.

The president-elect also had harsh words for the pro-Russia gunmen, comparing them to Somalian pirates.

“Their goal is to turn Donbass into a Somalia where they would rule with the power of machine guns. I will never allow that to happen on the territory of Ukraine,” Poroshenko said, adding that he hoped Russia would support his efforts to stabilize the east.

Poroshenko’s spokesman Andriy Zhigulin told the Associated Press that the date for his inauguration has not been set yet.

In Moscow, Foreign Minister Sergey Lavrov said Russia appreciated Poroshenko’s statements about the importance of Ukraine’s ties with Russia and his pledge to negotiate an end to fighting in the east.

“We are ready for dialogue with representatives of Kyiv, with Petro Poroshenko,” Lavrov said at a briefing, adding it was a chance that “cannot be wasted.” He emphasized that Moscow saw no need for any involvement by the United States or the European Union in those talks.

“We don’t need any mediators,” he said pointedly.

Lavrov also noted Russia’s longstanding call for the Kyiv government to end its military operation in eastern Ukraine.

The rebels had vowed to block Sunday’s voting in the east. Less than 20 percent of the polling stations were open there after gunmen intimidated residents by smashing ballot boxes, shutting down polling centers and issuing threats.

But nationwide, about 60% of Ukraine’s 35.5 million eligible voters turned out Sunday, and long lines snaked around polling stations in the pro-Western capital, Kyiv.

Joao Soares, special coordinator for the OSCE observer mission in Kyiv, hailed Sunday’s vote and “a clear resolve of the authorities which resulted in a genuine election largely in line with international commitments.”

“Ukrainian authorities should be commended for their efforts in the extraordinary circumstances to facilitate an election” which was held in parts of Ukraine’s volatile east, Soares said.

He said monitors did see multiple threats, intimidation and abduction of election officials in the east, which is overrun by pro-Russian militia.

With votes from 75% of the precincts counted Monday, Poroshenko was leading with about 54% in the field of 21 candidates. Former Prime Minister Yulia Tymoshenko was running a distant second with 13%. If those results hold, Poroshenko would avoid a runoff election next month. Election officials said official results would be announced by June 5.

Speaking to reporters, Poroshenko struck a tone of unity Monday, saying he had no “rivals or political opponents in the race” and all of the other main candidates have congratulated him on his win.

“More than ever, Ukraine now needs to be united,” he said.

The election, which came three months after pro-Moscow President Viktor Yanukovych was chased from office by crowds following months of street protests and allegations of corruption, was seen as a critical step toward resolving Ukraine’s protracted crisis.

Since his ouster in February, Russia has annexed the Crimea Peninsula in southern Ukraine, the eastern regions of Luhansk and Donetsk have declared their independence from Kyiv, and the interim Ukrainian government has launched an offensive in the east to quash an uprising.

The interim Kyiv government and the West have accused Russia of backing the separatist uprising. Moscow has denied the accusations.

President Barack Obama praised Ukrainians for participating in the voting “despite provocations and violence.” Obama said the U.S. supports Ukraine’s sovereignty and territorial integrity, rejects Russia’s “occupation and attempted annexation of Crimea” and is eager to work with the next president.